Subject of the invention is a device and method for drilling and making foundation pole piles with a ground-tamping technology, which permits the use of covering tubes for drilling polluted grounds.
A growing problem consists in making foundation piles in polluted grounds, generally in areas for industrial use.
The drilling and tamping technology, also known as “displacement”, is particularly used in presence of polluted grounds, as it permits to minimize the remaining material, that is the material exiting from the excavation necessary for making the pile. The works are so realized with the maximum respect of the environment and permit a relevant reduction of the costs, thanks to the fact that it is not necessary to dispose of great quantities of polluted ground, which necessarily requires special and very expensive treatments.
According to the present art, various drilling and tamping devices are known.
Patent EP-0228138 describes a drilling device which performs a tamping of the ground in a radial direction with respect to the drilling axis by means of a conical shaft which is provided with an elongated propeller extending up to the tip.
Patent EP-0664373 instead describes a drilling device provided with a fuse-shaped roller, loosely mounted on an axis inclined with respect to the rods of the drilling battery, which thanks to the rotation of the rods rolls on the surface of the excavation by tamping the ground.
It is always more frequently necessary to realize said drilling operation in presence of aquifer, which cannot be put into communication (for example when only the surface of one of them is polluted). Other times instead it can occur to drill in particularly unstable regions of ground (covering grounds) in which stabilization problems are encountered of the walls of the hole after the passage of the tool. It is therefore necessary to realize said drilling operation with the aid of a covering tube, which inhibits the collapse of the excavation but most of all inhibits the reflow/remix of waters coming from adjacent aquifers. This entails that the regions of ground already interested by the drilling operation remain totally insulated from the region in which the excavation is made, which generally is situated at the end region of the drilling device.
It is also necessary that said covering tube can be uncoupled from the tamping tool anytime during the drilling operation. In some situations it is in fact required to make piles starting from a lower height with respect to the ground level. Without being able to leave in the hole the covering tube after drilling, it would be necessary to cast concrete for the entire depth reached and then subsequently destroy the excess portion. This would be a waste of time, resources and material—either to be supplied or to be disposed of—with a consequent increase of the production costs.
Furthermore, when in presence of hard grounds or when particularly difficult layers must be crossed, the tamping tool is not able to advance and so it must be substituted with a digging tool to remove material, for example an auger or a bucket. In order to make such substitution, the tool has to be extracted from the hole by leaving the covering tube at the reached height.
In some situations the required depth of excavation is greater than the length necessary for the covering tube. In these cases, once having reached the value corresponding to the length of the tube, the tool must be disengaged from the tube, leaving it in place, and then continue the drilling operation. In the lifting/casting phase the tool is required to couple with the tube once again, in order to extract it from the hole.
Drilling devices are known, which permit the use of a covering tube.
Patents EP-0235105 and EP-1402146 show percussion drilling devices in which a digging tip, connected with a battery of rods, is generally combined with a bottom-hole hammer, and is able to drag a covering tube.
Such devices advance in the ground by the combined action of the percussion and the rotation. The debris produced in the region of the tip must be evacuated, as otherwise the tool would not be able to advance and they are conveyed at the surface, through the gap between the covering tube and the inner rod, by means of a fluid, generally water, for the perforation. This fluid is brought up to the perforating tip through channels internal to the tool.
Both mentioned devices are provided with a cutting means positioned on the digging tip, which make a hole having a diameter sufficient to advance the covering tube in the ground. In order to be able to extract the battery of rods and the digging tip from the covering tube, the counterbore element must be able to take configuration in which its maximum encumbrance is smaller than the internal diameter of the tube. For this reason its shape is of the eccentric kind, so that it can take two main positions: the working one, corresponding to the maximum diameter, and the closing one, corresponding to the minimum diameter.
In the operative phase, said digging head so has the function of enlarging the hole created by the drilling tip preceding it. This enlargement is realized with a removal of material, which is removed/detached from the walls of the excavation by means of digging/disrupting accessories. These means are usually teeth or bits. The first ones literally dig the ground, whereas the second ones breaks it up thanks to the high pressure generated with the contact between the same and the bit.
In any case, when making a drilling operation with removal of material, it happens that the hole created has a greater diameter with respect to that of the tool which has made the drilling operation. The excavation and the subsequent removal of the ground produce a loosening of all surrounding material of the hole, and also thanks to the action of the drilling fluid injected from the central duct, they create such a crumbling that an excavated hole is obtained, having much greater dimensions than those of the tool itself.
It is therefore evident that a gap is generated between the covering tube and the walls of the excavation realized by the reamer element. It is consequently impossible to separate the high regions of the battery from those of the excavation. During the crossing of an aquifer, water would have access to all other ground layers which are placed above and below it, and which are involved in the drilling operation. The same drilling fluid can act as a contaminant means. Therefore this kind of devices cannot be used in polluted grounds.
Furthermore, the field of application of the preceding patents being of the known art is that of the drilling operation with a bottom-hole hammer, which involves the excavation in particularly hard and rocky grounds, which therefore are generally stable. The presence of the tube is uniquely reserved to the first meters of excavation in which generally what is in jargon called “covering ground” is present, characterized by an incoherent matrix which tends to close upon the hole itself.
When this matrix has gone through, the excavation reaches rocky grounds and the tip must be adequately dimensioned in order to dig a hole much greater than the tube, so that it can insist on the bedrock without running aground.